1. Field of the Invention
The present invention relates to a miniaturized brush particularly adapted for medical use formed at the distal end of an elongated brush body having a hollow lumen formed therein and particularly to the construction, function and uses thereof.
2. Description of the Background Art
Commonly assigned, U.S. Pat. No. 5,370,653 to Cragg, incorporated herein by reference in its entirety, discloses a thrombectomy system for dissolving a soft fibrinous obstruction, such as a recently formed thrombus, within a patient's vascular system, either in a patent vein or artery or in a vascular implant, e.g. an A/V graft. The thrombectomy system employs rotating brush bristles within the thrombus to separate the fibrin of the thrombus from blood cells while mixing the separated fibrin with a dissolving or thrombolytic agent, e.g. streptokinase or urokinase, that is introduced at the same time into the separated fibrin.
The inventive rotating brush described in the '653 patent has flexible brush bristles extending outward from a brush shaft or drive shaft distal end in all directions. The brush is attached to the elongated, flexible, rotatable drive shaft or brush shaft which is attached at its proximal end to a drive motor to impart rotary motion to the brush shaft and bristles. The system includes a brush delivery catheter adapted to be introduced and advanced through a patient's blood vessels until the distal end is positioned adjacent the soft fibrinous thrombus. Once the brush delivery catheter is positioned, the brush bristles and brush shaft are passed through the brush delivery catheter lumen and out its distal opening to place the brush in contact with the soft thrombus. The bristles are sufficiently resilient and dimensioned for allowing compression and passage out of and back into the distal opening of the introducer lumen and for mixing into and macerating the fibrin of the soft thrombus, without damaging a vessel wall.
In one embodiment, the drive shaft is solid, and the dissolving agent is introduced through the brush delivery catheter lumen alongside the drive shaft lumen while the drive shaft is rotated. The thrombolytic agent is emitted from the distal end opening of the brush delivery catheter lumen in the region of rotation of the brush bristles for dissolving the soft thrombus exposed by the rotating brush bristles.
In another embodiment described in the '653 patent, the brush shaft is hollow to define a brush shaft lumen and preferably is formed with a penetrable distal tip valve normally closing the distal end opening of the brush shaft lumen. The thrombolytic agent is optionally delivered through the brush shaft lumen and through side exit holes or ports into the region of the brush bristles. The brush shaft lumen allows the introduction of the brush over a previously introduced and positioned guidewire so that the brush may be readily advanced to a thrombus in a blood vessel. Optionally, a microcatheter bearing a distal inflatable balloon or a mesh basket may be first placed in the vessel distal to the obstruction. The brush can then be introduced over the microcatheter and used while the inflated balloon or mesh basket placed distally of the brush bristles restrains the flow of fragments distally and allows the dissolving agent to complete the dissolution thereof. No particular construction of the hollow lumen drive shaft to achieve a small overall diameter is described in the '653 patent.
In German OLS DE 3921071, the use of a spiral wound brush that is rotated to wrap the fibrin of a thrombus in its bristles is described. In certain embodiments, the brush bristles are arranged in a spiral, screw pattern around either a solid core wire or a hollow tube with a lumen adapted to receive a guidewire. The brush bristles are rotated or otherwise advanced into a thrombus and then rotated to wind up the fibrin and separate it from blood cells. The particular manner of attaching the bristles to the solid core wire or hollow tube brush shaft is not described, nor is the use of a thrombolytic agent to dissolve the thrombus suggested.
Commonly assigned U.S. Pat. No. 5,681,355 to Serra et al., incorporated herein by reference in its entirety, discloses a hollow lumen, thrombectomy brush and method of fabrication which allows for the brush to be introduced over a previously placed guidewire into a very small blood vessel. The miniaturized brush is provided with an elongated, flexible, rotatable brush or drive shaft adapted to be attached at its proximal end to a drive motor for rotating the shaft. The drive shaft is formed with a proximal elongated section formed of a hollow, thin wall tube having an inner lumen and an outer surface and a distal section. The distal section comprises a hollow, thin wall tube extension having a coiled wire wound about it entrapping brush filaments between turns of the coiled wire and the outer wall of the hollow tube extension. The brush is formed of brush filaments, each having first and second ends and a predetermined length between the first and second ends, entrapped in a winding interface between turns of the coiled wire and the outer wall of the hollow tube extension in an entrapment zone intermediate the first and second ends. The brush filaments thereby each form first and second brush bristles extending separately outward from the entrapment zone to the first and second ends thereof.
The assignee of the '653 and '355 patents and the present application has implemented the solid drive shaft brush embodiment of the '653 patent in the Cragg Thrombolytic Brush.TM.. The Cragg Thrombolytic Brush.TM. is presently used in the lumen of an A/V graft implanted in a patient's vascular system for hemodialysis to dissolve thrombi that form therein. The Cragg Thrombolytic Brush.TM. is described and depicted in "The Thrombolytic Brush", by Andrew H. Cragg, MD presented at The Second Mid-Atlantic Conference on Angio Access: Establishment and Maintenance of Dialysis and Venous Access, Williamsburg, Va (pp. 162-165 of proceedings) in October 1996 and in product literature published by the assignee in 1997.
The brush and fabrication method disclosed in the '355 patent is meritorious but is expensive to produce. Moreover, the coiled wire entrapment of the brush bristles tends to make the side wall and outer diameter of the distal section larger than is desirable. This increased thickness, the angle of outward extension of the brush bristles from the entrapment zone and the stiffness of the bristles contribute to making it difficult to advance the brush through a 6 French or smaller diameter catheter lumen and out of the distal end opening thereof. A need exists for a simpler and less expensive fabrication process and resulting thrombolytic brush of this type.